NAME SERVICES

Names and addresses File names /etc/passwd URLS Internet domain names—dcs.qmw.ac.uk Identifiers- ROR, NFS File Handles Pure Name Impure Name

Names and addresses contd.. A name is resolved when it is translated into data about the named resource or object Name  Object is binding Names are bound to attributes of named object

Names and Services Names in DS-> specific to some service A client uses such a name when requesting a service to perform an operation upon a named service A filename -> FS A process identifier ->PMS

Name Services examples DNS maps domain name to the attributes of a host Computer X500 DS maps a person’s name into attributes including their address and telephone no CORBA NS maps a RO -> ROR

Composed naming domains used to access a resource from a URL WebExamples/earth.html 2:60:8c:2:b0:5a file

URL and URN URL-> A DNS computer name and path name Dangling link URN’s to solve dangling link Owner of a resource registers its name, along with its current URL with a URN look up service The owner registers the new URL if resource moves

URC URC – Uniform Resource Characteristic or Uniform Resource Citations are a subset of URNS An URC is a description of a Web Service consisting of attributes of the resource

Name Service Requirements To handle an arbitrary no of names and to serve an arbitrary no of administrative organizations A long lifetime High availability Fault Isolation

Name spaces A collection of all valid names recognized by a particular service Heirarchical name spaces Flat name spaces DNS names are called domain names DNS – Heirarchical Consists of one or more name components or labels seperated by deleimiter “.”

DNS Namespace contd The root is referred to as “.” Client software keeps a list of domain names that are appended automatically to any single component name before resolution

Naming Aliases Allowing a convenient name to be substituted for a more complicated one One domain name is defined to stand for another -> copper.dcs.qmw.ac.uk

Naming domains It is a name space for which there exist a single overall administrative authority for assigning names within it uk  ac.uk  qmw.ac.uk  dcs.qmw.ac.uk

Combining and Customising name spaces Merging Heterogeneity Customization

Name resolution Iterative name resolution Navigation –Iterative Multicast navigation –Nonrecursive –Recursive

Non-Recursive client NS1 NS2 NS3

Recursive Client NS1 NS2 NS3

Caching Client name resolution software and servers maintain a cache of the results of previous name resolutions Request is checked in the cache first Performance Availability

Domain Name System Domain names Dns queries –Host name resolution –Mail host name resolution –Reverse resolution –Host Information –Well known services

DNS Name Servers DNS naming data are divided into zones A zone contains the following data –Attribute data for names in domain –The name and addresses of at least two name servers ->authoritative data for the zone –The names of NS -> Sub domain –Zone management parameters

DNS name servers contd.. SA enter the data for a zone into a master file, which is source of authoritative data for the zone Two types of servers –Master server –Secondary server –TTL

DNS Resource Records A NS CNAME SOA WKS PTR HINFO MX TXT

Format Domainname ttl class type value 1D IN NSdnso 1D IN MX mail1.qmw.ac.uk www 1D IN CNAME copper copper 1D IN A dcs 1D IN NS dnso.dcs dnso.dcs 1D IN A